Methods and systems disclosed herein relate generally to forming a wet-etchable, sacrificial lift-off layer or layers compatible with high temperature processing, and forming a new product having a single or multi-layer film produced with this sacrificial layer.
In thin film processing, various situations arise when it is desirable to deposit a film on one substrate and eventually transfer it to another. The original substrate may be chosen for properties such as tolerance to high temperatures or coefficient of thermal expansion while the new substrate may be chosen for other properties such as flexibility. In such situations, a lift-off process may be used. A sacrificial film is applied to the original substrate prior to deposition of the lift-off layer. Such processes have been developed for epitaxial growth. (J. J. Schermer, P. Mulder, G. J. Bauhuis, M. M. A. J. Voncken, J. van Deelen, E. Haverkamp, and P. K. Larsen, “Epitaxial Lift-Off for large area thin film III/V devices,” Phys. Stat. Sol. (a), 202, pp. 501-508 (2005).) These methods are extremely expensive and only apply for substrates, sacrificial layers, and lift-off layers that are grown epitaxially. Processes have also been developed that use polymer lift-off layers that are compatible only with low temperatures. (V. Linder, B. D. Gates, D. Ryan, B. A. Parviz, and G. M. Whitesides, “Water-soluble sacrificial layers for surface micromachining,” Small, 1, pp. 730-736 (2005).)
There are not currently non-epitaxial methods for forming a sacrificial layer for liftoff that are tolerant to high temperatures. This technology is badly needed. For instance, in the field of thin film photovoltaics (PV), copper indium gallium diselenide (CIGS) is typically grown on a soda lime glass (SLG), optimally at a substrate temperature of 550° C. If one wants to grow CIGS on a flexible substrate such as polyimide (PI), the temperature must be lowered resulting in sub-optimal performance. What is needed is a lift-off process that would allow CIGS to be grown at high temperature and transferred to a PI substrate. The technology is also needed in the field of flexible electronics where the choice of materials is often limited to what temperature the flexible substrate can tolerate.